The present invention relates to a new and distinct hybrid variety of northern highbush blueberry (Vaccinium corymbosum L.) named ‘RYOKU NH-12’. This novel variety was found by open pollination of ‘Spartan’, ‘Duke’ and ‘Denies Blue’ in the tests conducted for the period from 2004 to 2008 in Matsumoto-City, Nagano-prefecture, Japan. As stated below, ‘RYOKU NH-12’ has apparently different characteristics from those of the ‘Spartan’ and ‘Duke’, both being widely planted and important varieties in the Chubu district of Japan.